Anthropogenic Aerosols and the Evolution of U.S. Droughts

Abstract:

Anthropogenic aerosols interact with solar radiation to influence regional to global climate. Trends in aerosol concentrations have impacted the evolution of surface air temperatures and the hydrological cycle over the last 150 years, but the magnitude of influence and any role in shaping extreme events remains uncertain. We use a general circulation model (GISS GCM ModelE) to study the impact of anthropogenic aerosols on the formation of two potential U.S. droughts. Two periods are analyzed, the 1930s Dust Bowl and the 1970s “missed drought”. Each period realized ocean conditions ripe for the formation of central U.S. drought, but experienced differing composition and amounts of anthropogenic aerosol forcing. Simulations forced solely by observed sea surface temperature and sea ice distributions reveal drier and warmer conditions in the central U.S. (annual decreases of up to 0.5 mm/day and warming of 0.5°C). We find that anthropogenic aerosols of the 1930s, containing a significant warming component from U.S. black carbon, exacerbated the warm conditions (0.2°C) and provided slightly drier conditions. In contrast, anthropogenic aerosols of the 1970s, containing a large cooling component from U.S. sulfate, reduced annual precipitation deficits and lowered temperatures by up to 0.4°C. Our results showcase the importance of anthropogenic aerosol forcing in the evolution of U.S. droughts.